>If you're a cannon main, finish your lvl100 upgrade quest if you haven't done so, and level up Devastation Shell to lvl60. This will decrease his combo rate (which will help A LOT) as well as decreasing his party's defence, which will help in poking a hole in the frontline.

A boss fight that normally takes people 3+ tries to win, took me only one try for me because of this. Although, I did it with lv46 D. Shell, iirc. If you have a spartan with leveled War Cry, use that to drop Servant Leader's combo rate.